Field of the Invention
The present invention relates to an endoscope system and specifically relates to an endoscope system capable of performing a normal (white light) observation using white light and a special light observation using special light.
Description of the Related Art
An endoscope system is used in recent years which applies specific narrow wavelength-band light (special light) to biological mucosa tissue to obtain tissue information at a desired depth of body tissue, or which can perform so-called a special light observation.
Using the special light observation, it is possible to visualize body information such, for example, as microstructure of a new blood vessel generated in a mucosa layer or a submucosa layer and enhancement of a lesion part, which information is difficult to obtain in a normal observation.
Upon changing of the observation mode from a normal observation mode of performing the normal observation to a special light observation mode of performing the special light observation, illumination light is changed from white light to special light, and image processing of generating an observation image which is to be displayed on a monitor apparatus from an imaging signal acquired by an imaging sensor is changed from image processing suitable for the normal observation mode to image processing suitable for the special light observation mode.
In the special light observation mode, since narrow-band light limited to a specific narrow wavelength region is used, there can be a case where sufficient light amount is not obtained. In such a case, deterioration of image quality of the observation image caused by shortage of the illumination light amount (darker observation image in the special light observation mode relative to the observation image in the normal observation mode) is concerned.
Japanese Patent Application Laid-Open No. 2011-010998 (hereinafter referred to as Patent Literature 1) discloses, in an endoscope apparatus including a blue laser light source and a violet laser light source, control of the light sources of calculating brightness information from an imaging signal obtained from an imaging element and increasing or decreasing an emitting light amount of each light source such that the image signal is at a desired brightness level.
Japanese Patent Application Laid-Open No. 2009-148487 (hereinafter referred to as Patent Literature 2) discloses, for an endoscope apparatus including a light source section that changes illumination light wavelength bands by switching filters and performing light amount control of holding brightness of an image displayed on a monitor constant, a technology of preventing large disorder in the monitor image in switching of an observation mode and enhancing response of switching of the observation mode by fixing the emitted light amount to the value immediately before switching in switching of the observation mode (in switching of the filters) and suspending the light amount control.
Japanese Patent Application Laid-Open No. 2012-050641 (hereinafter referred to as Patent Literature 3) discloses an endoscope system of controlling switching timing from image processing for a normal observation to image processing for a special light observation according to chronological response characteristics of a light source for the special light observation in switching from a normal observation mode to a special light observation mode.
Japanese Patent Application Laid-Open No. 2012-029703 (hereinafter referred to as Patent Literature 4) discloses an endoscope apparatus configured capable of continuously controlling each of emitted light amounts of narrow-band light and white light independently and configured to apply both of the white light and the narrow-band light at an arbitrary emitted light amount ratio for imaging and to set an object to be observed with narrow-band light (superficial vessels, gland ducts and the like) in the obtained observation image at the most suitable brightness level such that brightness values do not saturate over the whole observation image.
Japanese Patent Application Laid-Open No. 2004-024611 (hereinafter referred to as Patent Literature 5) discloses, for a fluorescent observation image processing apparatus including a fluorescent image mode and a normal image mode, image processing of performing signal processing corresponding to each mode.